Regensburg 2002 – wissenschaftliches Programm
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O: Oberflächenphysik
O 22: Adsorption an Oberfl
ächen (II)
O 22.1: Vortrag
Dienstag, 12. März 2002, 16:15–16:30, H36
Structure and dynamics of Na adsorption on Al(100) — •Mikael Borg1,2, Catherine Stampfl2, Anders Mikkelsen1, Edvin Lundgren1, David L. Adams3, Matthias Scheffler2, and Jesper N. Andersen1 — 1Dept of Synchr Radiation Research, P.O. Box 118, S-221 00 Lund, Sweden — 2Fritz-Haber-Institut der Max-Planck-Gesellschaft , Faradayweg 4-6, D-14195 Berlin-Dahlem, Germany — 3Institute of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark
The adsorption of 0.2 monolayers (ML) of Na on Al(100) has been studied both experimentally, using low energy electron diffraction (LEED) and high resolution core level spectroscopy (HRCLS), and theoretically, using density functional theory (DFT). It is found that this system has two ordered phases: Deposition of Na at low temperature results in the formation of islands of c(2×2) symmetry, with Na atoms occupying four-fold hollow sites. By annealing the sample at 300 K, and cooling the sample to 100 K, the Na atoms form a (√5×√5)R27∘ structure occupying surface substitutional sites. The transition from hollow to substitutional adsorption is irreversible.
The (√5×√5)R27∘ structure with substitutionally adsorbed Na undergoes a reversible order-disorder phase transition at ∼230 K. To investigate this system further, we performed additional DFT calculations for a wide range of coverages (from 0.0625 to 0.5 ML), for adsorption in both the hollow and substitutional sites, from which we extract interaction energies which are used in a lattice gas Monte Carlo simulation.